Topic: Portrait by Duncan Grant

Thee is a portrait painting by Duncan Grant circulating on Pinterest.  Unfortunately it has no reference to date or the sitter's name.  I am anxious to complete the attribution and also intrigued to know the background of this painting.  The sitter is a black man in a blue suit, red waistcoat, white shirt and black tie.  He is raising his right arm as if to make a point.  The wooden chair has armrests and there is a brown framed window behind.  The background is olive and grey with a touch of pink.  It may be early (1918) and appears to be unfinished.

I would appreciate any leads on this matter.  Thank you, victoria cooper.